Field of the Invention
The present invention relates to a liquid discharge head that discharges liquid, such as ink.
Description of the Related Art
A recording method using a liquid discharge head, such as an inkjet recording head, involves supplying thermal and vibration energy to liquid, such as ink, and discharging the ink in the form of micro-droplets through discharge ports to form an image on a recording medium. A method for manufacturing such an inkjet head is disclosed in Japanese Patent Laid-Open No. 2002-019120.
In the manufacture of a liquid discharge head of this type, first, discharge energy generating elements and wiring conductors for supplying power to the discharge energy generating elements are mounted on a silicon substrate. Then, after a protective film is provided over the wiring conductors, an ink flow path and ink discharge ports are patterned with a resist. Next, a through hole (ink supply port) for supplying ink from the back side of the silicon substrate to the discharge energy generating elements is formed in the silicon substrate.
The resultant recording element substrate is attached to a support plate made of alumina or the like, so that the recording element substrate is electrically joined to an electric wiring member.
Next, a perimeter sealant is applied to protect side faces of the recording element substrate from ink and dust. After the perimeter sealant is cured, an inner lead bonding (ILB) sealant (electric-connection sealant) for sealing electric connections is applied over the perimeter sealant.
Functions required of the two sealants used here, the perimeter sealant for sealing around the perimeter of the recording element substrate and the electric-connection sealant, are as follows.
The perimeter sealant is required to quickly flow through a gap with a width of nearly 1 mm between a part on the support plate and the recording element substrate, and to fill the gap in a short time. Additionally, the perimeter sealant is required to protect the recording element substrate from ink and other things.
The electric-connection sealant is required not only to seal electric connections, but also to be resistant to rubbing with a blade or wiper for cleaning the area of ink discharge ports and to contact with paper caused by a paper jam.
A method for applying the two types of sealants, the perimeter sealant and the electric-connection sealant, is disclosed in Japanese Patent Laid-Open No. 2005-132102. This document describes a method in which a hardness of the electric-connection sealant after curing is higher than that of the perimeter sealant after curing and a main component and a curing agent of the electric-connection sealant are the same as those of the perimeter sealant.
With this method, even when the perimeter sealant and the electric-connection sealant are cured at the same time, it is possible to avoid competition for the curing agent (curing inhibition) between the sealants caused by a difference in curing speed.
In recent years, there has been a demand for inexpensive liquid discharge heads capable of printing high-resolution images at high speeds. An effective way for a liquid discharge head to record high-resolution images is to increase the integration density of discharge energy generating elements to a high level. Using inks with high color developing properties is also effective. An effective way to achieve high-speed printing is to increase the number of energy generating elements and increase the length of the liquid discharge head.
FIG. 3A is a diagram of a long and high-density inkjet recording head, as viewed from a direction in which ink is discharged. FIG. 3B is a cross-sectional view taken along line IIIB-IIIB in FIG. 3A. A recording element substrate 1 is provided with two ink supply ports 16 and four rows of discharge ports. The two ink supply ports 16 are filled with the same type of ink, which is then discharged therefrom.
In this inkjet recording head, the two ink supply ports 16 extending in the longitudinal direction of the recording element substrate 1 are arranged in parallel, and the recording element substrate 1 is long in length. Therefore, side faces of the central part of the recording element substrate 1 in the longitudinal direction are structurally sensitive to stress.
The electric-connection sealant has the function of protecting leads and thus has a high elastic modulus (high hardness). The perimeter sealant has a hardness lower than that of the electric-connection sealant. However, since the perimeter sealant contains the same main component and curing agent as those of the electric-connection sealant, the perimeter sealant has to have a certain degree of hardness. Because the perimeter sealant is in contact with ink, it may absorb the ink and swell depending on the use environment. As a result, stress may be applied to side faces of the central part of the recording element substrate 1.
Such a configuration in which stress is applied to the side faces of the central part of the recording element substrate 1 by swelling of the perimeter sealant has not been seen as a problem. However, when the length and the density of the head are further increased, the resulting stress may deform the recording element substrate 1 and flow path members 17, and may negatively affect the print quality. Flexibility in ink selection may be lost, and high image quality with good color developing properties may not be achieved.